Chemical Thermodynamics of Tin - Volume 12 - OECD Nuclear ...

338
A Discussion of selected references
The potential difference of these cells were measured at 15, 25 and 35 °C in a
concentration range of 1.0, 2.0, 3.0, 4.0 M HClO 4 and 0.017 to 0.11 M Sn(ClO 4 ) 2 . The
standard potentials found at 15 (− 141.5 mV), 25 (− 144.5 mV) and 35 °C (− 146.8 mV)
were used to calculate Δ
fG ο
m(Sn 2+ , 298.15 K) = − (27.87 ± 0.08) kJ·mol –1 ,
Δ
rS ο
m
(A.51) = − (51.1 ± 9.6) J·K –1·mol –1 , and S ο m (Sn 2+ , 298.15 K) = − (27.6 ± 9.6)
J·K –1·mol –1 .
While the value of Δ f
G ο
m
(Sn 2+ , 298.15 K) is close to the one selected by
CODATA [1989COX/WAG] (− (27.60 ± 0.40) kJ·mol –1 ) the value of S ο m
(Sn 2+ ,
ο
298.15 K) has been obtained by deriving ∂E
/ ∂ T from only three data pairs. It deviates
considerably from the CODATA value (− (16.7 ± 4.0) J·K –1·mol –1 ) and cannot be
recommended for selection.
Vasil’ev and Glavina’s experimental data have been re-evaluated with the SIT
model. The densities of HClO 4 solutions at t = 15 and 35 °C were interpolated from the
data given at 10, 20 and 30, 40 °C in [1989LOB], respectively. This SIT analysis, see
Figure A-33, Figure A-34, Figure A-35, resulted in a value for Δ
fG ο
m(Sn 2+ , 298.15 K) =
− (28.01 ± 0.13) kJ·mol –1 , slightly different to the one given by Vasil’ev and Glavina. In
addition the values of ε(Sn 2+ , ClO − 4
) were calculated for 15, 25 and 35 °C (see
Table A-27).
Figure A-33: SIT analysis of the data of [1973VAS/GLA] at 15 °C (: experimental
data, error bars (± 0.5 mV) estimated by the reviewer; solid line: linear fit; dotted lines:
95% confidence limits).
{E m
°' + [RT·ln(10)/2F]·2D}/mV
-140
-142
-144
-146
-148
-150
Sn 2+ + H 2
(g) Sn(s) + 2H +
E°(Sn 2+ /Sn) = –(141.49 ± 0.82) mV
Δε = (0.047 ± 0.009) kg·mol –1
-152
0 1 2 3 4 5
m(ClO – 4 )/mol·kg–1
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012